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there, I'm in a bit of pickle and was hoping someone could provide some assistance. I have a mail server, [sending.server.com] trying to send to another server to [target.server.com] from [[email protected]], but I get the following response from [target.server.com]

[[email protected]]
    host [target.server.de] [ipv4 address]
    SMTP error from remote mail server after RCPT TO:<[[email protected]]>:
    550 5.7.1 <[[email protected]]>: Recipient address rejected:
    Mail appeared to be SPAM or forged. Ask your Mail/DNS-Administrator to correct HELO and DNS MX settings or to get removed from DNSBLs; MTA helo:
    [sending.server.com], MTA hostname: unknown[incorrect IPv4 address of sending.server.com] (helo/hostname mismatch)

I checked quite a few DNSBLs, and [sending.server.com] is not any of them. And weirder still, this happens from only a few of the email addresses from [sending.server.com]. [sending.server.com] uses postfix. And the responses only started recently, it is a first encountering such a problem.

Many thanks for any ideas on how to go about solving this.

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    Well...what about fixing this: helo/hostname mismatch?
    – gxx
    May 9, 2016 at 22:25
  • I was wondering about that, too, but anark10n noted that only some sending email addresses were being blocked, which doesn't seem to support an overall server error.
    – Thomas N
    May 10, 2016 at 14:27
  • I did try to solve this issue by getting a PTR record configured, but supervisor keeps stonewalling on who to contact to get it done. Would a PTR record resolve this issue?
    – anark10n
    May 12, 2016 at 7:05

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For whatever reason [target.server.com] has decided to administratively disallow email from specific addresses on [sending.server.com]. This is the cause of the SMTP 550 5.7.1 error code you're seeing. You need to contact the mail administrators using [target.server.com]'s established process to see why they are doing so. They are the only ones who can lift the ban for your users. The email addresses, postmaster@[target.server.com] and\or abuse@[target.server.com] are fairly standard avenues for this that should be monitored.

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  • Looking at the response, it seems the it's coming from [sending.server.com] and not [target.server.com]. More specifically, [[email protected]]. Is there something wrong with this?
    – anark10n
    May 13, 2016 at 13:19
  • I'm not seeing that in the examples you gave in your question. However, that's the process that's reporting back to you, the sender. The remote server giving the error certainly doesn't know how to reach you, so your MTA fills that role. And yes, this is normal.
    – Thomas N
    May 13, 2016 at 15:46
  • Ok, figured as much and just wanted to make sure. Also checked what's in my helo by sending to [email protected] and this what I got: [email protected] host mail.abuseat.org [54.93.50.35] SMTP error from remote mail server after RCPT TO:<[email protected]>: 550 *** The HELO for IP address [incorrect ipv4 address] was '[sending.server.com]' (valid syntax) ***
    – anark10n
    May 16, 2016 at 7:31

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